cam (8) moves the lockup mode shift fork rearward along with the lockup shift collar assembly
(2). The lockup shift assembly sleeve (2) locks the mainshaft (1) to the drive sprocket (3). Torque
is sent by the chain (6) to the front output shaft (7) and to the front axle. The torque distribution
in this mode is now determined by vehicle dynamic conditions and weight distribution. The
planetary differential is not operating and both the front and rear propeller shafts are being driven
at equal RPM, therefore giving a 4 high lock mode. This mode should only be used for extra
traction during off road use. Using this mode on dry pavement causes tire scuffing.
4LO Lock Mode Power Flow
Fig. 150: 4LO Lock Mode Power Flow Diagram
Courtesy of GENERAL MOTORS CORP.
When the BW 4493, shown or the BW 4494, shown in inset, shifts the transfer case to the 4LO
Lock mode, it commands the encoder motor (7) to turn the shift cam shaft (8), to rotate the shift
cam (9). The range cam profile on the shift cam (9) moves the high/range shift fork (10) and the
high/low range sleeve (4) rearward to the 4LO Lock range position. The high/low range sleeve
(4) outer teeth disengage from the input shaft (1) high-speed teeth. The high/low range sleeve (4)
2007 Hummer H3
2007 TRANSMISSION Transfer Case - BW 4493/4494 - H3